Electrical resistance tubular heating conductor with axially varying power distribution

ABSTRACT

An electrical resistance tubular heating conductor of axially varying power distribution having a constant wall thickness body and an axially varying metal coating thereon is made by depositing the metal coating in an axial direction at a varying rate.

United States Patent [191 Von Holzen Nov. 26, 1974 ELECTRICAL RESISTANCE TUBULAR HEATING CONDUCTOR WITH AXIALLY VARYING POWER DISTRIBUTION Inventor:

A ssignee:

Filed:

Appl. No.:

Gerhard Von Holzen, Erbslet, Switzerland Gesellschaft Zur Fordenung Der Forschung an der Eidg. John Hochschule, Zurich, Switzerland Nov. 7, 1972 Foreign Application Priority Data Nov. 19, 1971 Switzerland 16858/71 US. Cl. 219/553, 117/71 M, ll7/2l2, 219/543, 338/89, 338/142, 338/195, 338/217, 338/308 b 3/10, H05b 3/42 Field of Search 219/388, 530, 543,553; 338/89, 90, 138, 140, 142, 195, 217, 218, 308; 29/620; 57/34; 117/71 M, 212

5/1937 Germany 338/217 Primary Examiner--Volodymyr Y. Mayewsky Attorney, Agent, or Firm-Browdy and Niemark [57] ABSTRACT An electrical resistance tubular heating conductor of axially varying power distribution having a constant wall thickness body and an axially varying metal coating thereon is made by depositing the metal coating in an axial direction at a varying rate.

5 Claims, 3 Drawing Figures Ill/l/ll/l/l/ll/l/l/ll/l////// I ELECTRICAL RESISTANCE TUBULAR HEATING CONDUCTOR WITH AXIALLY VARYING POWER DISTRIBUTION The present invention concerns a current-bearing heating conductor whose power distribution varies axially and which comprises a metallic tubular body of at least approximately constant wall thickness and provided with a metal layer of axially varying thickness, and further concerns a method of manufacture thereof and a system for the performance of the said method.

Tests are being performed in suitable circuits for the purpose of investigating the heat transfer from reactor fuel elements to the surrounding coolant. For such tests it is necessary instead of the reactor fuel elements to use electrically heated elements which simulate as accurately as possible the distribution of heat production such as arises in the nuclear reactor owing to the neutron flowdistribution. Generally, the heat production varies along the elements in the form of a continuous function, such as a cosine function.

The manufacture of heating tubes with axially varying power distribution has hitherto mainly applied the following two methods:

1. Heating elements are built up in stairway fashion from individual tubular pieces joined up by welding or soldering. This results in a tube of discontinuously varying wall thickness. The heating power, following the local wall thickness distribution, is therefore also distributed in stairway fashion. This method can only give an approximation of the distribution required. Moreover, it is highly labor intensive and provides heating elements of low mechanicalstrength.

2. The secondmethod consists in machining a tube around its outer diameter by grinding or turning,'with the object of achieving the varying wall thickness necessary for the power distributionrequired. This method is very expensive and demands a high degree of accuracy in the machining process.

The object of the present invention is to provide a firstclass product as well as a cheaper and simple method for the manufacture thereof. Accordingly, the heating conductor claimedhereunder is characterized in that the body and the metal layer are directly interconnected metallically.

The invention is now to be described by way of example with reference to the accompanying drawings, i which FIG. 1 shows a longitudinal section through a heating conductor;

FIG. 2 shows a system for the manufacture of heating conductors according to FIG. 1, with the principal system units represented;

eter of 8.35 millimeters and an outside diameter of 9.5

millimeters, for instance, while the thickness of the layer 3 may be 20 microns at the end of the body tube 1 and 0 micron in the middle, for instance. Viewed in longitudinal section, the thickness variation may follow a cosine function. g

The heating tube shown in FIG. 3 presents a difference of 2.54 times between the highest local power in the tube middle and the lowest local power at the tube ends. After coating, the silver layer 3' may be protected by providing it and the body tube 1' with a thin-walled tube 5 which is drawn on or hammered on.

Such a heating element may be manufactured galvanically as follows, for-instance:

A galvanizing chamber 9, preferably made of PVC, through which flows an electrolyte 7, such a silver cyanide solution, and which contains an annular silver electrode 11 is longitudinally moved'along a body tube 1 at a varying rate. The chamber 9 is sealed by O-rings 10 with respect to the body tube. The rate of advance of the chamber 9 is determined by a frequencycontrolled drive 15 controlled by a sound tapebearing a previously recorded program, as later explained. The program is produced by tone generators. During the process, the tube 1 to be coated is rotated at constant speed by a drive 16, in order to produce a layer 3 which is uniformly thick around the circumference.

Accordingly, the points where the rate of advance of the chamber 9 is slow receive a greater layer thickness 0', and vice versa.

Immediately before and behind the chamber 9, the tube 1 is rinsed with water from pipes 17 for the purpose of removing any residual electrolyte from the surface of the tube or heating conductor. The system is arranged in a collecting tank 19.

With the galvanizing station in operation, the electrolyte 7 circulates through the system. For this, a pump 27 draws the electrolyte from an electrolyte container 25, and a pressure controller 28 fitted into the pipe 30 serves to control the circulation quantity of the electrolyte 7. The return flow is effected through the return pipe 32 to the electrolyte container 25. The system is arranged on a stand 21 presenting lateral bearing supports 22 and 23 which stand in the collecting tank 19, as shown in FIG. 2. The electric connection is effected from the positive pole 34 direct to the silver electrode 1 1, while the negative pole 35 is connected to the bearing support 23.

To produce the aforesaid program tape for the control of the advance rate, the program is first recorded on a sound tape, which is then used to control the chamber. For this purpose, it is necessary to calculate the variation of the layer thickness and the advance rate in accordance with the given axial power distribution of the heat medium, in particular a reactor fuel element. The next step is to calculate the variation of the control frequency in correlation with time: f (t). Finally, the function f (t) found is recorded on the sound tape intended for control. This results in a sound tape bearing the control frequency correlated with time, f (t),'which can be used to control the feed motor of the drive 15. Accordingly, the entire system, comprising electrolyte 7, chamber 9, silver electrode 11 and drive 15, moves in a programmed fashion ensuring that the layer 3 is deposited to the varying thickness required.

In principle, though, it is possible instead to provide a body tube 1 with a layer 3 by vacuum vapor-coating or by some thermal spray method. This can be carried rial having approximately constant wall thickness,

and a metallic layer of electrical resistance material coated on said tubular body and metallically and integrally connected thereto, said metallic layer forming a tube and being of continuously axially varying thickness, largest at both ends, and having an axial section appearing as a smooth bent curve.

2. The heating conductor of claim 1, wherein said metallic layer is connected to said tubular body galvanically.

3. The heating conductor'of claim I, wherein said metallic layer is interconnected to said tubular body by vacuum vapor coating.

4. The heating conductor of claim 1, further comprising a protective tube located over said metallic layer.

5. The heating conductor of claim 1, wherein the thickness of said metallic layer, viewed in axial section,

appears as a cosine function. 

1. An electrical resistance heating conductor having an axially varying electrical power distribution, comprising: a metallIc tubular body of electrical resistance material having approximately constant wall thickness; and a metallic layer of electrical resistance material coated on said tubular body and metallically and integrally connected thereto, said metallic layer forming a tube and being of continuously axially varying thickness, largest at both ends, and having an axial section appearing as a smooth bent curve.
 2. The heating conductor of claim 1, wherein said metallic layer is interconnected to said tubular body galvanically.
 3. The heating conductor of claim 1, wherein said metallic layer is interconnected to said tubular body by vacuum vapor coating.
 4. The heating conductor of claim 1, further comprising a protective tube located over said metallic layer.
 5. The heating conductor of claim 1, wherein the thickness of said metallic layer, viewed in axial section, appears as a cosine function. 